Structures 3 Exam Preparation PDF

## Structures 3 Exam Preparation ### Material Selection for Structural Elements **Concrete:** - High compressive strength, ideal for beams and foundations. - Durability in diverse environmental conditions. **Concrete Compressive Strength is expressed as fck:** - Example C25/30 means: - C25: C...

## Structures 3 Exam Preparation ### Material Selection for Structural Elements **Concrete:** - High compressive strength, ideal for beams and foundations. - Durability in diverse environmental conditions. **Concrete Compressive Strength is expressed as fck:** - Example C25/30 means: - C25: Characteristic compressive strength of a cylinder (150 mm diameter x 300 mm height) = 25 MPa. - 30: Characteristic compressive strength of a cube (150 mm x 150 mm x 150 mm) = 30 MPa. - The cylinder strength is lower than the cube strength due to different testing conditions and stress distributions. | Concrete Grade | Application | |---|---| | C12/15 | For non-structural or lightweight applications | | C25/30 | Standard structural concrete | | C30/37, C35/45, C40/50, etc | For higher-strength applications like bridges or large structures | ### Examples in the Exam **Why is the reinforced concrete bonding not on the bottom of the ground floor slab?** | - Dry wall | | - Normal force | **How do you make sure that the load doesn't get transferred?** - Don't close the wall completely. Use a small foam that only transfers the vibrations. | - Point load: Column along the main axis | | - Area load: Slab and foundation | | - Live loads | | - Dead loads | | - Wind and snow load | | - Line loads | | - Beam - Shear force & momentum | **How do you calculate the reaction force?** - Equilibrium. ### Timber - Renewable, moderate strength, used in low-rise buildings. - Environmentally friendly material. **Characteristic bending strength E.g. C16 = 16 MPa:** - C16: Used in general construction where loads are moderate. - Examples: Internal framing, studwork, and roof joists in residential buildings. **Advantage: More cost-effective than higher grades:** - C24: Used in structural applications requiring higher strength. - Examples: Load-bearing beams, floor joists, and outdoor structures like decking. **Advantage: Can handle greater spans and loads compared to C16:** - Considerations: - Load types and material strength - Environmental conditions (e.g. moisture, exposure to weather) - Cost and material availability ### Steel - High tensile and compressive strength, ideal for frames and structural supports. - Excellent ductility. **Tensile strength means:** - High tensile and compressive strength. - The maximum stress steel can withstand while being stretched or pulled before breaking. - Measured in Megapascals (MPa) or pounds per square inch (psi). **Yield strength:** - The stress at which steel begins to deform plastically (permanently). Below this point, the steel returns to its original shape when the load is removed. - Yield strength is often less than tensile strength. | Material | Yield strength (MPa) | |---|---| | S235 | 235 (for 16 mm thickness) | | S355 | 355 (for 16 mm thickness) | ### Safety factors | Material | Load | |---|---| | Concrete | Dead loads = 1.35 | | Steel | Permanent actions = 1.35 | | Timber | Variable actions = 1.5 | | | | |---|---| | - Live loads, snow load, wind load | | - Architects = 1.4 | | - Design load, qd = q x Y Load | - Purpose: These safety factors are simplified for architects, ensuring safe designs without detailed engineering calculations. - Design Stress, σd = Fy/γ material - Should be bigger than σd - Beam design thumb rule: - Beam dimensions: - width (b): Typically b = L/15 or L/20 - depth (d): Typically d = L/12 or L/15 - Example calculation (for a 5-meter span): - width (b) = 350 mm (rounded from 333 mm) - depth (d) = 450 mm (rounded from 417 mm) - Reinforcement: - Minimum steel area = 0.2% of cross-sectional area. ### Foundation **Types of foundations:** - Point foundations: for isolated loads (eg. columns) - Stip foundations: for continuous loads (eg. walls) - Slab foundations: for large buildings or poor soil **Conditions:** - Selecting the right foundations: considering building load and soil conditions. - Use strip foundations for long walls, point foundations for isolated columns. **Foundation sizing:** - Width of strip foundation: b = P/g, P = External load, g = soil bearing capacity. - Foundation depth: d = δ/2. **For slab foundations:** - Typically, 300-500 mm depth for low-rise buildings. **Load transfer in a truss:** - The top chord is in compression, while the bottom chord is in tension. - Loads are transferred through the diagonal members to the supports. **Key concepts:** Trusses provide efficient load transfer using material. **Eurocodes:** - Eurocode 2: Concrete design - Eurocode 3: Steel design - Eurocode 5: Timber design **Key focus:** - Basic load combinations and material strength. - Simplified safety factors (eg. 1.4 for all loads).